There are some problems with the existing organic light-emitting displays. Organic light-emitting diodes (OLEDs) are current-driven devices that require a steady current to control light emission. Driving transistors in each OLED pixel circuit may have different threshold voltages due to e.g. fabrication processes and device aging, resulting in each OLED exhibiting different luminance for the same data signal. This may lead to uneven luminance among different display areas.